1. Field of the Invention
The present invention is a multi-dies stacked package structure, more particularly; it is a zigzag-stacked package structure.
2. Description of the Prior Art
In recent years, the semiconductor package process is using three-dimension (3D) package method to have relative large integrated semiconductor or the volume of the memory in the less measure of area. In order to achieve this object, the die stacked method is used to have 3D package structure.
In the prior art, the stacked structures of the dies are formed by stacking a plurality of dies one another and on a substrate and wire bonding the dies and the substrate for electrical connection. FIG. 1a is a sectional view showing a zigzag-stacked package structure with the dies of a similar size in the prior art. As shown in FIG. 1a, the zigzag-stacked package structure 100 includes a circuit substrate 110, dies 120aand 120b, a spacer 130, a plurality of wires 140 and an encapsulated material 150. The circuit substrate 110 includes a plurality of pads and the die 120a and die 120b respectively includes a plurality of pads 122a and 122b. The pads 122a and 122b are arranged around the periphery areas of the die 120a and 120b respectively. The die 120a is disposed on the circuit substrate 110 and the die 120b is disposed on top of the die 120awith the spacer 130 placed therebetween. The wires 140 connect the pads 112 on the circuit substrate 110 with the pads 122aand 122bby wire bonding process and the dies 120a and 120b are then electrically connected to the circuit substrate 110. The encapsulated material 150 is formed on the circuit substrate 110 to cover the wires 140, the dies 120a and 120b. 
Because the pads 122a and 122b are arranged on the periphery areas of the dies 120a and 120b , the die 120a is not able to directly support the die 120b. So, in the package process, after the die 120a is connected to the circuit substrate 110, the pads 122a on the die 120a are connected to the pads 112 on the circuit substrate 110 by a wire bonding process. The spacer 130 is then connected to the die 120a and the die 120b is connected on the spacer 130. The pads 122b on the die 120b are connected to the pads 112 on the circuit substrate 110 by another wire bonding process. Obviously, the spacer 130 is disposed between the die 120a and 120b to provide a distance between the die 120a and 120b for the wires 140. However, the usage of the spacer 130 causes the difficulty to reduce the thickness of the zigzag-stacked package structure 100.
Besides, another zigzag-stacked package structure with different die sizes is provided in prior art, as the sectional view shown in FIG. 1B. The zigzag-stacked package structure 10 includes a circuit substrate 110, die 120c, die 120d, a plurality of wires 140 and an encapsulated material 150. The circuit substrate 110 includes a plurality of pads 112. The size of the die 120c is bigger than the size of the die 120d. The dies 120c and 120d respectively include a plurality of pads 122c and 122d. The pads 122c and 122d are arranged on the periphery areas of the dies 120c and 120d . The die 120c is disposed on the circuit substrate 110 and the die 120d is disposed on the die 120c. The wires 140 connect the pads 112 with the pads 122c by wire bonding process and the die 120c is then electrically connected to the circuit substrate 110. The wires 140 connect the pads 112 with the pads 122d by wire bonding process and the die 120d is then electrically connected to the circuit substrate 110. The encapsulated material 150 is formed on the circuit substrate 110 to cover the wires 140, the dies 120c and 120d. 
Because the die 120d is smaller than the die 120c, the die 120d does not completely cover the die 120c when the die 120d is disposed on the die 120c. Therefore, the package process is different to the process in FIG. 1A. Both of the dies 120c and 120d are mounted on the substrate 110 first and then a one-time wire bonding process is then executed. When the dies with different sizes are stacked together to form a zigzag-stacked package structure in prior art, the sizes of the dies on top should be gradually smaller; therefore, the number of the dies to be stacked is limited.
According to the two stacked structures described above, the design and the usage of the dies are limited. According to the problems above, U.S. Pat. Nos. 6,252,305, 6,359,340 and 6,461,897 provide another zigzag-stacked package structure, as shown in FIG. 1C. Obviously, the package structure uses the dies with the same size but no spacer 130 to separate the dies. However, during the stacking steps, the dies are stacked to each other by using at least two types of pad arrangement. For example, the pads on the first dies are disposed on one side of the first dies and the pads on the second dies are disposed on two adjacent sides. Besides, the package structure needs the wire bonding process to be executed in two directions. Therefore, as the structure shown in FIG. 1C, it would increase the time of wire bonding process and it would cause asymmetrical molding flow during the molding process. The wire in one direction may be hit by the transversal molding strength causing the contact of the wires and further the malfunction of the dies.
Besides, U.S. Pat. No. 6,900,528, U.S. Pat. No. 20030137042A1, U.S. Pat. No. 20050029645A1and U.S. Pat. No. 20060267173A1disclosed another zigzag-stacked package structure. Obviously, the height between the dies is used to replace the spacer to increase the density of the package structure. However, there are some problems in the manufacture of the package structure. After two dies are connected together, the first wire bonding process shall be proceeded before another dies can be stacked upon. When the number of dies is increased, the package process become more time-consuming and more complicated.